The art of laminating layers of glass and interposed polymeric materials to produce "safety glass" laminates has been practiced for many years by the manufacturers of automobile windshields. Such composites effectively reduced the serious injuries that had previously resulted from bodily ejection from an automobile through a shattered single pane windshield upon impact during an accident. However, the glass and polymer, i.e., polyvinyl butyral, composites still were likely to cause severe lacerations and cosmetic disfigurement due to flying pieces of broken glass or bodily contact with the windshield.
Thereafter, anti-lacerative windshields were developed, having one or more layers of glass substrate and a layer of polymeric material bonded to the inside surface of the windshield facing the passenger compartment. This configuration provided a substantial improvement in safety by placing a shock absorbent layer of material between the glass windshield and the automobile passengers. It eliminated the likelihood of flying glass particles within the passenger compartment upon impact during an accident, and provided a body impact surface that aided the deceleration of a person thrust against the windshield, thereby reducing his or her susceptibility to lacerations. In addition, it reduced laceration by avoiding direct body contact with broken glass.
Although several methods exist for the bonding of a polymeric material to the inner surface of an automobile windshield, the art has not developed into an industry-wide standard because of the problems encountered in producing an optically transparent laminate. More specifically, manufacturers have found it difficult to form the exposed surface of the polymeric material so that it is at all points parallel to the surface of the glass substrate, and optically clear.
One method of manufacture involves the use of a glass cover plate which substantially conforms to the predetermined curvature of a glass windshield substrate. The cover plate is contacted to the surface of a film of thermoplastic polyurethane, which in turn is intimately contacted to a glass windshield substrate. Pressure is applied to the cover plate in order to laminate the thermoplastic polyurethane film to the glass windshield substrate, and to impress a smooth, optically transparent surface onto the surface of the polyurethane layer. Such an operation requires a release agent which allows the cover plate to easily and cleanly part from the polyurethane layer, following a laminating process employing severe conditions of high temperature and pressure over a long period of time, without affecting the smooth image impressed by the cover plate onto the polyurethane layer.